U.S. patent number 5,994,887 [Application Number 08/982,648] was granted by the patent office on 1999-11-30 for low power consumption constant-voltage circuit.
This patent grant is currently assigned to Mitsumi Electric Co., Ltd.. Invention is credited to Naoshi Tokuda.
United States Patent |
5,994,887 |
Tokuda |
November 30, 1999 |
**Please see images for:
( Certificate of Correction ) ** |
Low power consumption constant-voltage circuit
Abstract
A constant-current generating circuit, a power-source voltage
being applied thereto, generates a constant current. A voltage
generating circuit element is connected between the
constant-current generating circuit and a fixed voltage point, is
supplied with the constant current which is generated by the
constant-current generating circuit, and generates a constant
voltage. A control circuit detects the current generated by the
constant-current generating circuit, and, using the detected
current, controls the constant-current generating circuit so that
the current to be supplied to the voltage generating circuit
element is the constant current.
Inventors: |
Tokuda; Naoshi (Atsugi,
JP) |
Assignee: |
Mitsumi Electric Co., Ltd.
(Tokyo, JP)
|
Family
ID: |
18177018 |
Appl.
No.: |
08/982,648 |
Filed: |
December 2, 1997 |
Foreign Application Priority Data
|
|
|
|
|
Dec 5, 1996 [JP] |
|
|
8-325451 |
|
Current U.S.
Class: |
323/313;
323/315 |
Current CPC
Class: |
G05F
3/222 (20130101) |
Current International
Class: |
G05F
3/08 (20060101); G05F 3/22 (20060101); G05F
003/16 () |
Field of
Search: |
;323/311,312,313,314,315 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Sterrett; Jeffrey
Attorney, Agent or Firm: Ladas & Parry
Claims
What is claimed is:
1. A constant-voltage circuit comprising:
a first resistor, the power-source voltage being applied to one end
thereof;
a first transistor, the emitter thereof being connected with the
other end of said first resistor;
a second transistor, the junction type thereof being the same as
that of said first transistor, the power-source voltage being
applied to the emitter of said second transistor, the collector of
said second transistor being connected with the base of said first
transistor;
a second resistor, connected between the emitter and base of said
second transistor;
a third resistor, connected between the base and collector of said
second transistor;
a third transistor, the junction type thereof being different from
that of said first transistor, the collector of said third
transistor being connected with the collector of said first
transistor, the collector and base of said third transistor being
connected with one another, the emitter of said third transistor
being connected with a voltage generating means;
a fourth transistor, the junction type thereof being different from
that of said first transistor, the collector of said fourth
transistor being connected with the collector of said second
transistor, the base of said fourth transistor being connected with
the base of said third transistor;
a fourth resistor, one end thereof being connected with the emitter
of said fourth transistor, and the other end of said fourth
resistor being connected to said voltage generating means;
a fifth transistor, the junction type thereof being the same as
that of said first transistor, the emitter of said fifth transistor
being connected with the connection point between said first
resistor and the emitter of said first transistor, the base of said
fifth transistor being connected with the base of said first
transistor;
a sixth transistor, the junction type thereof being different from
that of said fifth transistor, the collector of said sixth
transistor being connected with the collector of said fifth
transistor, the base and collector of said sixth transistor being
connected with one another, and the emitter of said sixth
transistor being grounded;
a constant-current source, which is supplied with the power-source
voltage, for generating a constant current;
a seventh transistor, the junction type of which is different from
that of said fifth transistor, the constant current generated by
said constant-current source being supplied to the collector of
said seventh transistor, the base thereof being connected with the
base of said sixth transistor;
a fifth resistor, one end thereof being connected with the emitter
of said seventh transistor and the other end thereof being
grounded; and
an eighth transistor, the junction type thereof being the same as
that of said fifth transistor, the base of said eighth transistor
being connected with the connection point between said
constant-current source and the collector of said seventh
transistor, the emitter of said eighth transistor being connected
with the collectors of said first transistor and said third
transistor, and the collector of said eighth transistor being
grounded.
2. A constant-voltage circuit comprising:
a constant-current generating means, to which a power-source
voltage is applied, for generating a constant current;
a voltage generating means, which is connected between said
constant-current generating means and a fixed voltage point and is
supplied with the constant current which is generated by said
constant-current generating means, for generating a constant
voltage; and
a control means for detecting the current generated by said
constant-current generating means, and, using the detected current,
controlling said constant-current generating means so that the
current to be supplied to said voltage generating means is the
constant current;
wherein said constant-current generating means comprises:
a first resistor, the power-source voltage being applied to one end
thereof;
a first transistor, the emitter thereof being connected with the
other end of said first resistor;
a second transistor, the junction type thereof being the same as
that of said first transistor, the power-source voltage being
applied to the emitter of said second transistor, the collector of
said second transistor being connected with the base of said first
transistor;
a second resistor, connected between the emitter and base of said
second transistor;
a third resistor, connected between the base and collector of said
second transistor;
a third transistor, the junction type thereof being different from
that of said first transistor, the collector of said third
transistor being connected with the collector of said first
transistor, the collector and base of said third transistor being
connected with one another, the emitter of said third transistor
being connected with said voltage generating means;
a fourth transistor, the junction type thereof being different from
that of said first transistor, the collector of said fourth
transistor being connected with the collector of said second
transistor, the base of said fourth transistor being connected with
the base of said third transistor; and
a fourth resistor, one end thereof being connected with the emitter
of said fourth transistor, and the other end of said fourth
resistor being connected to said voltage generating means.
3. The constant-voltage circuit, according to claim 2, wherein said
control means comprises:
a fifth transistor, the junction type thereof being the same as
that of said first transistor, the emitter of said fifth transistor
being connected with the connection point between said first
resistor and the emitter of said first transistor, the base of said
fifth transistor being connected with the base of said first
transistor;
a sixth transistor, the junction type thereof being different from
that of said fifth transistor, the collector of said sixth
transistor being connected with the collector of said fifth
transistor, the base and collector of said sixth transistor being
connected with one another, and the emitter of said sixth
transistor being grounded;
a constant-current source, which is supplied with the power-source
voltage, for generating a constant current;
a seventh transistor, the junction type of which is different from
that of said fifth transistor, the constant current generated by
said constant-current source being supplied to the collector of
said seventh transistor, the base thereof being connected with the
base of said sixth transistor;
a fifth resistor, one end thereof being connected with the emitter
of said seventh transistor and the other end thereof being
grounded; and
an eighth transistor, the junction type thereof being the same as
that of said fifth transistor, the base of said eighth transistor
being connected with the connection point between said
constant-current source and the collector of said seventh
transistor, the emitter of said eighth transistor being connected
with the collectors of said first transistor and said third
transistor, and the collector of said eighth transistor being
grounded.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a constant-voltage circuit, and,
in particular, to a constant-voltage circuit which generates a
constant voltage from a power-source voltage.
2. Description of the Related Art
FIG. 1 shows an example of a circuit arrangement in the related
art.
A constant-voltage circuit 11 in the related art includes a
reference voltage generating circuit 12, a voltage detecting
circuit 13, a comparing circuit 14, and a transistor Q11. The
reference voltage generating circuit 12 generates a reference
voltage Vref from a power-source voltage Vcc. The voltage detecting
circuit 13 detects a detected voltage Vs in accordance with a
constant output voltage Vout. The comparing circuit 14 compares the
reference voltage Vref generated by the reference voltage
generating circuit 12 and the detected voltage Vs detected by the
voltage detecting circuit 13 with one another. The transistor Q11
draws current into the ground from an output terminal Tout in
accordance with the comparison result of the comparing circuit
14.
The power-source voltage Vcc is lowered through a resistor R11 by a
voltage drop and supplied to the reference voltage generating
circuit 12, voltage detecting circuit 13, comparing circuit 14 and
transistor Q11.
The reference voltage generating circuit 12 is connected between
the resistor R11 and the ground GND,and includes a resistor R12 and
a Zener diode Dz which are connected in series. The reference
voltage Vref, which is the Zener voltage of the Zener diode Dz, is
output from the connection point Pref between the resistor R12 and
Zener diode Dz.
The voltage detecting circuit 13 is connected between the resistor
R11 and the ground GND, and includes resistors R13 and R14 which
are connected in series. The voltage, obtained as a result of the
power-source voltage Vcc being lowered by the voltage drop, is
divided, and, thus, the detected voltage Vs is output from the
connection point Pvs between the resistors R13 and R14.
The reference voltage Vref generated by the reference voltage
generating circuit 12 is supplied to the inverting terminal (-) of
the comparing circuit 14, and the detected voltage Vs detected by
the voltage detecting circuit 13 is supplied to the non-inverting
terminal (+) of the comparing circuit 14. The comparing circuit 14
outputs the differential voltage (Vs-Vref) between the detected
voltage Vs and the reference voltage Vref.
The output voltage of the comparing circuit 14 is supplied to the
base of the transistor Q11. The transistor Q11 is an NPN
transistor, the collector thereof being connected to the connection
point between the resistor R11 and the output terminal Tout, and
the emitter thereof being grounded.
The transistor Q11 increases its emitter current as a result of a
rise of the output voltage of the comparing circuit 14. As a
result, the current supplied to the output terminal Tout decreases.
The transistor Q11 decreases its emitter current as a result of a
fall of the output voltage of the comparing circuit 14. As a
result, the current supplied to the output terminal Tout
increases.
For example, when the power-source voltage Vcc rises, the output
voltage Vout rises, and the detected voltage Vs detected by the
voltage detecting circuit 13 also rises. As a result of the rise of
the detected voltage Vs, the output voltage of the comparing
circuit 14, which is the differential voltage (Vs-Vref) between the
detected voltage Vs and the reference voltage Vref, thus rises.
As a result the rise of the differential voltage (Vs-Vref) of the
comparing circuit 14, the base voltage of the transistor Q11 rises.
Because the transistor Q11 is the NPN transistor, as a result of
the rise of its base voltage, its emitter current increases, and
thereby, the current drawn through the transistor Q11 into the
ground GND increases. As a result of the increase of the current
drawn through the transistor Q11 into the ground GND, the current
which is supplied to a load (not shown in the figure) decreases.
Thereby, the output voltage Vout falls.
By the above-described operations, the output voltage Vout is
maintained to be constant.
When the power-source voltage Vcc falls, the output voltage Vout
falls, and the detected voltage Vs detected by the voltage
detecting circuit 13 also falls. As a result of the fall of the
detected voltage Vs, the output voltage of the comparing circuit
14, which is the differential voltage (Vs-Vref) between the
detected voltage Vs and the reference voltage Vref, thus falls.
As a result of the fall of the differential voltage (Vs-Vref) of
the comparing circuit 14, the base voltage of the transistor Q11
falls. Because the transistor Q11 is the NPN transistor, as a
result of the fall of its base voltage, its emitter current
decreases, and thereby, the current drawn through the transistor
Q11 into the ground GND decreases. As a result of the decrease of
the current drawn through the transistor Q11 into the ground GND,
the current which is supplied to a load (not shown in the figure)
increases. Thereby, the output voltage Vout rises.
By the above-described operations, the output voltage Vout is
maintained to be constant.
However, in the constant-voltage circuit in the related art, energy
consumption occurs as a result of the current flowing through the
Zener diode which generates the reference voltage, resistors which
are used for detecting the output voltage, the comparing circuit
which compares the reference voltage and the output voltage with
one another, and the output controlling transistor Q11 which
controls the output voltage as a result of bypassing the current in
accordance with the output voltage of the comparing circuit.
Further, in the constant-voltage circuit in the related art, when
the output voltage rises, the emitter current of the transistor
increases. Thereby, the current supplied to the output terminal
Tout is reduced. Thus, the output voltage Vout is maintained to be
constant. Accordingly, as shown in FIG. 2, when the power-source
voltage rises, the current (useless current) directly flowing to
the ground GND increases. Thus, it is difficult to reduce current
consumption.
For example, when the constant output voltage 1 V is obtained,
approximately 1 .mu.A is consumed in the Zener diode, approximately
0.5 .mu.A is consumed in the resistors and comparing circuit,
approximately 0.5 .mu.A is consumed in the output controlling
transistor Q11. Thus, a total of 2 .mu.A is uselessly consumed.
SUMMARY OF THE INVENTION
The present invention has been devised in consideration of the
above-mentioned points. An object of the present invention is to
provide a constant-voltage circuit which can be driven with low
current consumption.
The present invention comprises:
a constant-current generating means, to which a power-source
voltage is applied, for generating a constant current;
a voltage generating means, which is connected between the
constant-current generating means and a fixed voltage point and is
supplied with the constant current which is generated by the
constant-current generating means, for generating a constant
voltage; and
a control means for detecting the constant current generated by the
constant-current generating means, and, using the detected constant
current, controlling the constant-current generating means so that
the constant current to be supplied to the voltage generating means
is constant.
In the arrangement, the control means controls the constant current
generated by the constant-current generating means, and thus,
controls the current supplied to the voltage generating means.
Thus, the constant voltage is generated by the voltage generating
means. Because the constant current is always supplied to the
voltage generating means for generating the constant voltage, even
if the power source voltage increases, the current flowing through
the voltage generating means is the constant current. Accordingly,
it can be prevented that the useless current increases.
Other objects and further features of the present invention will
become more apparent from the following detailed description when
read in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a circuit arrangement of one example of the related
art;
FIG. 2 shows a characteristic graph of useless current with respect
to power-source voltage in the example of the related art;
FIG. 3 shows a circuit arrangement of one embodiment of the present
invention;
FIG. 4 shows a characteristic graph of useless current with respect
to power-source voltage in the embodiment of the present invention;
and
FIG. 5 shows a circuit arrangement of a reference voltage circuit
portion in the embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 3 shows a circuit arrangement of one embodiment of the present
invention.
A constant-voltage circuit 1 in the embodiment includes a reference
voltage circuit portion 2, a starting-up circuit portion 3, and a
control circuit portion 4. The reference voltage circuit portion 2
generates a reference voltage Vref from a power-source voltage Vcc.
The starting-up circuit portion 3 starts up the reference voltage
circuit portion 2. The control circuit portion 4 controls the
reference voltage Vref which is generated by the reference voltage
portion 2.
The reference voltage circuit portion 2 includes resistors R1, R2,
R3, R4, R5, PNP transistors Q2, Q3, and NPN transistors Q4, Q5. The
reference voltage circuit portion 2 generates the reference voltage
Vref which is temperature-compensated in accordance with the
power-source voltage Vcc. The resistors R1, R2, R3 and R4 act as a
first resistor, a second resistor, a third resistor and a fourth
resistor, respectively. The resistor R5 acts as a constant-voltage
generating means.
Further, the transistors Q2, Q3, Q4 and Q5 act as a first
transistor, a second transistor, a third transistor and a fourth
transistor, respectively.
The starting-up circuit portion 3 includes a constant-current
source 3a, NPN transistors Q9, Q10, and diodes D1, D2. The
starting-up circuit portion 3 draws current from the reference
voltage circuit portion 2 and the control circuit portion 4, and
starts up the reference voltage circuit portion 2 and the control
circuit portion 4.
The control circuit portion 4 includes a constant-current source
4a, a resistor R6, and PNP transistors Q1, Q6, Q7, Q8. The control
circuit portion 4 performs control in accordance with the
power-source voltage Vcc so that current to be supplied to the
resistor R5 of the reference voltage circuit portion 2 is constant.
The control circuit portion 4 acts as control means. The
transistors Q1, Q7, Q8 and Q6 act as a fifth transistor, a sixth
transistor, a seventh transistor and an eighth transistor,
respectively.
Operations of the circuit will now be described.
When the power-source voltage Vcc is applied, by the
constant-current source 3a of the starting-up circuit portion 3 and
the constant current source 4a of the control circuit portion 4,
constant currents I2 and I1 flow through the starting-up circuit
portion 3 and the control circuit portion 4, respectively. As a
result of the constant current I2 flowing through the starting-up
circuit portion 3, the constant current I2 is supplied to the
diodes D1 and D2. Thereby, the base voltage of the transistor Q10
rises.
Because the transistor Q10 is the NPN transistor, as a result of
the rise of the base voltage, the transistor Q10 turns on. As a
result of the transistor Q10 turning on, the transistor Q10 draws
current out from the base of each of the transistors Q1 and Q2.
Because the transistors Q1 and Q2 are the PNP transistors, each of
the transistors Q1 and Q2 turns on as a result of current being
drawn out from the bases thereof.
As a result of each of the transistors Q1 and Q2 turning on,
current is supplied to the collector and the base of each of the
transistors Q4 and Q7. Because the transistors Q4 and Q7 are the
NPN transistors, each of the transistors Q4 and Q7 turns on as a
result of the current being supplied to the base of each of the
transistors Q4 and Q7.
The collector and base of the transistor Q4 are connected to the
base of the transistor Q5, and the transistors Q4 and Q5 form a
current-mirror circuit. Thereby, as a result of the transistor Q4
turning on, the transistor Q5 also turns on.
The emitter of the transistor Q4 is connected to the resistor R5,
and, as a result of the transistor Q4 turning on, current is
supplied to the resistor R5. Further, the emitter of the transistor
Q5 is connected to the resistor R5 via the resistor R4, and the
transistor Q5 supplies current to the resistor R5.
As a result of the current being supplied to the resistor R5, the
reference voltage Vref appears across the resistor R5. The
reference voltage Vref is output from a reference voltage output
terminal Tvref.
Further, the collector and the base of the transistor Q7 are
connected to the bases of the transistors Q8 and Q9. Thus, a
current-mirror circuit is formed by the transistors Q7 and Q8, and
a current-mirror circuit is formed by the transistors Q7 and Q9.
Accordingly, as a result of the transistor Q7 turning on, each of
the transistors Q8 and Q9 turns on. The emitter of the transistor
Q8 is grounded via the resistor R6, and the collector of the
transistor Q8 is connected to the connection point between the
constant-current source 4a and the base of the transistor Q6.
Accordingly, as a result of the transistor Q8 turning on, current
is drawn out from the base of the transistor Q6. Because the
transistor Q6 is the PNP transistor, as a result of the current
being drawn out from the base, the transistor Q6 turns on.
Further, the collector and emitter of the transistor Q9 are
connected to the two ends of the diode D2, respectively. The
transistor Q9 turns on as a result of the transistor Q7 turning on.
As a result, the base voltage of the transistor Q10 falls, and,
thereby, the transistor Q10 turns off. Thus, the reference voltage
circuit portion 2 and the control circuit portion 4 are started
up.
Although the transistor Q10 has turned off as mentioned above, the
transistor Q5 is turned on as mentioned above. As a result, the
transistor Q5 draws current from the base of each of the
transistors Q1 and Q2. Accordingly, the on state of each of the
transistors Q1 and Q2 is maintained.
When, for example, the power-source voltage Vcc rises, the
collector current of each of the transistors Q4 and Q5 increases.
As a result of the increase of the collector current of each of the
transistors Q4 and Q5, the current supplied to the resistor R5
increases. As a result, the reference voltage Vref rises.
At this time, the voltage of the connection point between the
resistors R2 and R3 rises. Thereby, the collector current of the
transistor Q3 decreases. As a result of the decrease of the
collector current of the transistor Q3, the base voltage of each of
the transistors Q1 and Q2 falls.
As a result of the fall of the base voltage of the transistor Q1,
the collector current of the transistor Q1 increases. As a result
of the increase of the collector current of the transistor Q1, the
current supplied to the base of the transistor Q7 increases. As a
result, the collector current of the transistor Q7 increases, and
also, the collector current of the transistor Q8 increases. As a
result, the current drawn out from the base of the transistor Q6
increases. As a result of the increase of the current drawn out
from the base, the emitter current of the transistor Q6 increases.
As a result of the increase of the emitter current of the
transistor Q6, the current supplied to the base of each of the
transistor Q4 and Q5 decreases. As a result, the emitter current of
each of the transistors Q4 and Q5 decreases. Thereby, the current
supplied to the resistor R5 decreases, and thus, the reference
voltage Vref falls.
By the above-described operations, the reference voltage Vref is
maintained to be a predetermined level (for example, 1 V).
When the power-source voltage Vcc falls and the collector current
of each of the transistors Q4 and Q5 decreases, the current
supplied to the resistor R5 decreases and the reference voltage
Vref falls. At this time, the voltage of the connection point
between the resistors R2 and R3 falls. Thereby, the collector
current of the transistor Q3 increases.
As a result of the increase of the collector current of the
transistor Q3, the base voltage of each of the transistors Q1 and
Q2 rises. As a result of rise of the base voltage of the transistor
Q1, the collector current of the transistor Q1 decreases. As a
result of the decrease of the collector current of the transistor
Q1, the current supplied to the base of the transistor Q7
decreases.
As a result of the decrease of the current supplied to the base of
the transistor Q7, the collector current of the transistor Q7
decreases, and also, the collector current of the transistor Q8
decreases. As a result, the current drawn out from the base of the
transistor Q6 decreases. As a result of the decrease of the current
drawn out from the base, the emitter current of the transistor Q6
decreases. As a result of the decrease of the emitter current of
the transistor Q6, the current supplied to the base of each of the
transistors Q4 and Q5 increases. As a result, the emitter current
of each of the transistors Q4 and Q5 increases. Thereby, the
current supplied to the resistor R5 increases, and thus, the
reference voltage Vref rises.
By the above-described operations, the reference voltage Vref is
maintained to be a predetermined level (for example, 1 V).
In the above-described constant-voltage circuit 1, all the constant
current generated through the resistors R1, R2, R3 and R4 and the
transistors Q2, Q3, Q4 and Q5 of the reference voltage circuit
portion 2 is supplied to the resistor R5 which is provided for
generating the reference voltage Vref. Thereby, the reference
voltage Vref is generated, and the control of the reference voltage
Vref is performed by controlling the current to be supplied to the
resistor R5 to be constant. Accordingly, the current flowing to the
ground can be maintained to be constant. Thus, useless current can
be prevented from increasing.
FIG. 4 shows characteristics of useless current with respect to the
power-source voltage Vcc in the embodiment of the present
invention.
As shown in FIG. 4, in the embodiment, because the control is
performed so that the current flowing through the resistor R5 is
constant, although the power-source voltage Vcc rises, the useless
current is maintained to be constant. Thus, the useless current can
be prevented from increasing.
Further, in the reference voltage circuit portion 2, temperature
compensation is performed.
A temperature compensation operation of the reference voltage
circuit portion 2 will now be described with reference to a
figure.
FIG. 5 shows a circuit arrangement of the reference voltage circuit
portion of the embodiment of the present invention.
In FIG. 5, Is represents the current flowing through the resistor
R2 and R3 from the power source voltage Vcc. I12 represents the
emitter current of the transistor Q2. I13 represents the emitter
current of the transistor Q3. I14 represents the collector current
of the transistor Q4. I15 represents the collector current of the
transistor Q5. Vref represents the reference voltage appearing
across the resistor R5.
In FIG. 5, the currents I14 and I15 are supplied to the resistor R5
from the transistors Q4 and Q5. Accordingly, the reference voltage
Vref appearing across the resistor R5 is expressed as follows:
VBEQ2 represents the voltage between the base and the emitter of
the transistor Q2. VBEQ3 represents the voltage between the base
and the emitter of the transistor Q3. When the circuit including
the transistors Q2, Q3 and the resistors R1, R2, R3 is considered,
the following equation holds:
From the equation (2), the voltage VR1=R1.multidot.I12 is expressed
as follows:
Generally, the voltage VBE between the base and the emitter of a
transistor is expressed by the following equation: ##EQU1## where k
represents Boltzmann's constant, T represents the absolute ambient
temperature, q represents the electronic charge, A represents the
emitter junction area, and I represents the emitter current.
When the equation (3) is rewritten using the equation (4), the
equation (3) can be expressed as follows: ##EQU2## where A2
represents the emitter junction area of the transistor Q2, and
A3represents the emitter junction area of the transistor Q3.
Further, VBEQ4 represents the voltage between the base and the
emitter of the transistor Q4. VBEQ5 represents the voltage between
the base and the emitter of the transistor Q5. When the circuit
including the transistors Q4, Q5 and the resistor R4 is considered,
the following equation holds:
From the equation (6), the voltage VR4=I15.multidot.R4 appearing
across the resistor R4 is expressed by the following equation:
When the equation (7) is rewritten using the equation (4), VR4 can
be expressed as follows: ##EQU3## where A4 represents the emitter
junction area of the transistor Q4, and A5represents the emitter
junction area of the transistor Q5.
In the equation (8), when it is considered that the current
amplification h.sub.FE of each of the transistors Q2 and Q4 is
sufficiently large, I12=I14.
Accordingly, the equation (8) becomes the following equation (9):
##EQU4##
Further, the equation (1), Vref=R5.multidot.(I14+I15) can be
expressed as follows:
From the equation (5), the current I12 can be expressed as follows:
##EQU5##
Further, from the equation (9), the current I15 can be expressed as
follows: ##EQU6##
When the equation (10) is rewritten using the equations (11) and
(12), the reference voltage Vref can be expressed as follows:
##EQU7##
When the equation (13) is differentiated by the temperature T, the
following equation (14) is obtained: ##EQU8##
In the equation (14), the second term ##EQU9## is a negative
value.
Accordingly, in the first term ##EQU10## the resistances of the
resistors R1, R4, R5, and the junction areas A2, A3, A4, A5 of the
transistors Q2, Q3, Q4, Q5 are appropriately set so that the
equation (14) is set to zero.
Thereby, it can be prevented that change of the temperature causes
the reference voltage Vref to change.
In the embodiment, the constant current generated by the resistors
R1, R2, R3, R4 and the transistors Q2, Q3, Q4, Q5 is supplied to
the resistor R5, and the reference voltage Vref is generated using
the voltage drop in the resistor R5. Thereby, the useless current
in the reference voltage circuit portion 2 can be reduced.
Further, in the starting up circuit portion 3 and control circuit
portion 4, the constant-current sources supply the minimum
necessary current and the portions are driven, respectively.
Accordingly, the useless current can be reduced to the minimum
necessary amount.
Further, temperature compensation is performed in the reference
voltage circuit portion 2, and thus, it can be prevented that
change of the temperature causes the reference voltage Vref to
change.
Further, the present invention is not limited to the
above-described embodiments, and variations and modifications may
be made without departing from the scope of the present
invention.
* * * * *